Compressed air is supplied from an air pressure source to a pneumatic actuator via a pneumatic circuit, the pneumatic actuator converting fluid energy to mechanical energy like a pneumatic cylinder or the like. The pneumatic circuit is provided with a filter for removing dusts or moisture in the compressed air supplied from the air pressure source, an also provided with a regulator for adjusting pressure of the compressed air supplied to the pneumatic actuator. Further, when the compressed air is supplied to the pneumatic actuator after a mist lubricant is injected into the compressed air, a lubricator is provided in the pneumatic circuit.
Fluid apparatuses such as a filter and a regulator are mutually coupled detachably to be utilized as an air treatment unit in order to facilitate maintenance and inspection of the fluid apparatuses and they are provided in the pneumatic circuit. A connector is used for mutually coupling the fluid apparatuses detachably in an air-tight manner. The connector includes a member which has a through-hole and seal faces and is disposed between fluid ports of respective fluid apparatuses and a member which mutually fastens fluid apparatuses adjacent to each other, and the fluid apparatuses are joined to each other by the connector in an air-tight manner and are caused to communicate with each other through the through-hole. Such connectors are described in Patent Documents 1 to 3, for example.    Patent Document 1: Japanese Patent Application Laid-Open Publication (Translation of PCT Application) No. 09-501756    Patent Document 2: Japanese Patent No. 2715049    Patent Document 3: Japanese Patent No. 2902389